I’ve always been a fan of the classic Helly Hansen Lifa Dry base layers (the ones with the stripes down the side) but I’ve seen some online workmen’s / trade supply sites offering another style called the Kastrup base layer for a lot cheaper.

On paper the specs look almost identical (polypropylene Lifa material) but the price is almost half as much.

Anyone using / had any experience with?

i have some helly workwear stuff, not sure if its the kastrup or not, i wear a lot of the lifa dry stuff as well,
to me the workwear stuff seems marginally thinner, but that may be because its white and my lifa is black or blue, and they it doesnt have the stripes down the arms
not overly helpful i know, but theres very little in it IMO, except price but you can get lifa twin packs for £40

Are they the same sizing/fitting? Or is it bigger and baggier?

I see Screwfix have the Kastrup tops for £12 (but limited sizes).

I’d say baggier, the arms are at least (builders probably have bigger arms than cyclists?)